Quantization parameter signaling for joint chroma residual mode in video coding

ABSTRACT

An example method includes decoding, from an encoded video bitstream, a sequence parameter set (SPS) referred to by one or more pictures of video data, wherein decoding the SPS comprises: parsing, at a first position in the SPS, a syntax element that indicates whether joint coding of chroma residuals is enabled or disabled for the one or more pictures of video data referring to the SPS; and parsing, at a second position in the SPS that is after the first position, one or more syntax elements representing a quantization parameter (QP) mapping table.

This application claims the benefit of U.S. Provisional Application No.62/907,401, filed Sep. 27, 2019, the entire contents of which areincorporated by reference herein.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

In one example, a method of decoding video data includes decoding, froman encoded video bitstream, a sequence parameter set (SPS) referred toby one or more pictures of video data, wherein decoding the SPScomprises: parsing, at a first position in the SPS, a syntax elementthat indicates whether joint coding of chroma residuals is enabled ordisabled for the one or more pictures of video data referring to theSPS; and parsing, at a second position in the SPS that is after thefirst position, one or more syntax elements representing a quantizationparameter (QP) mapping table; decoding, from the encoded videobitstream, a picture parameter set (PPS) referred to by a picture of theone or more pictures of video data, wherein decoding the PPS comprises:parsing a syntax element that indicates whether a QP offset for jointlycoded chroma residuals is included in a chroma QP offset table andwhether a syntax element that specifies an offset to a luma quantizationparameter Qp′_(Y) used for deriving Qp′_(CbCr) is coded; and decodingthe picture based on the SPS and the PPS.

In another example, a device for decoding video data includes a memoryconfigured to store at least a portion of an encoded video bitstream;and one or more processors that are implemented in circuitry andconfigured to: decode, from the encoded video bitstream, a SPS referredto by one or more pictures of video data, wherein, to decode the SPS,the one or more processors are configured to: parse, at a first positionin the SPS, a syntax element that indicates whether joint coding ofchroma residuals is enabled or disabled for the one or more pictures ofvideo data referring to the SPS; and parse, at a second position in theSPS that is after the first position, one or more syntax elementsrepresenting a QP mapping table; decode, from the encoded videobitstream, a PPS referred to by a picture of the one or more pictures ofvideo data, wherein, to decode the PPS, the one or more processors areconfigured to: parse a syntax element that indicates whether a QP offsetfor jointly coded chroma residuals is included in a chroma QP offsettable and whether a syntax element that specifies an offset to a lumaquantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) is coded;and decode the picture based on the SPS and the PPS.

In another example, a method for encoding video data includes encoding,in an encoded video bitstream, a SPS referred to by one or more picturesof video data, wherein encoding the SPS comprises: encoding, at a firstposition in the SPS, a syntax element that indicates whether jointcoding of chroma residuals is enabled or disabled for the one or morepictures of video data referring to the SPS; and encoding, at a secondposition in the SPS that is after the first position, one or more syntaxelements representing a QP mapping table; and encoding, in the encodedvideo bitstream, a PPS referred to by a picture of the one or morepictures of video data, wherein encoding the PPS comprises: encoding asyntax element that indicates whether a QP offset for jointly codedchroma residuals is included in a chroma QP offset table and whether asyntax element that specifies an offset to a luma quantization parameterQp′_(Y) used for deriving Qp′_(CbCr) is coded.

In another example, a device for encoding video data includes a memoryconfigured to store at least a portion of an encoded video bitstream;and one or more processors that are implemented in circuitry andconfigured to: encode, in the encoded video bitstream, a SPS referred toby one or more pictures of video data, wherein, to encode the SPS, theone or more processors are configured to: encode, at a first position inthe SPS, a syntax element that indicates whether joint coding of chromaresiduals is enabled or disabled for the one or more pictures of videodata referring to the SPS; and encode, at a second position in the SPSthat is after the first position, one or more syntax elementsrepresenting a QP mapping table; and encode, in the encoded videobitstream, a PPS referred to by a picture of the one or more pictures ofvideo data, wherein, to encode the PPS, the one or more processors areconfigured to: parse a syntax element that indicates whether a QP offsetfor jointly coded chroma residuals is included in a chroma QP offsettable and whether a syntax element that specifies an offset to a lumaquantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) is coded.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages of the disclosure will be apparent from the description anddrawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure, and a corresponding coding tree unit(CTU).

FIG. 3 is a block diagram illustrating an example video encoder that mayperform the techniques of this disclosure.

FIG. 4 is a block diagram illustrating an example video decoder that mayperform the techniques of this disclosure.

FIG. 5 is a flowchart illustrating an example method for encoding acurrent block.

FIG. 6 is a flowchart illustrating an example method for decoding acurrent block.

FIG. 7 is a flowchart illustrating an example method for coding acurrent block of video data.

DETAILED DESCRIPTION

In general techniques of this disclosure are directed to techniques forsignaling parameters for joint coding of chroma residuals when coding ofvideo data. Residual data for a chroma block may be separately signaledas a Cb residual block and a Cr residual block. However, in someexamples, the Cb residual block and the Cr residual block may be jointlysignaled in what is referred to as a joint chroma coding mode. In thejoint chroma coding mode, a video encoder may encode a single jointchroma residual block and a video coder may derive a Cb residual blockand a Cr residual block from the single joint chroma residual block.

The availability of the joint chroma coding mode may be controlled byone or more syntax elements. For instance, a video coder may signal asyntax element in a parameter set a that indicates whether joint codingof chroma residuals is enabled or disabled for the one or more picturesof video data referring to the parameter set (e.g.,sps_joint_cbcr_enabled_flag).

A video coder may signal mapping tables that provide parameters forderiving chroma quantization parameter (QP) from acollocated/corresponding luma QP. The video coder may signal multiplemapping tables that may be used in different scenarios. For instance,the video coder may signal a Cb mapping table, a Cr mapping table, and ajoint Cb-Cr mapping table. However, arrangements that always signal allthree mapping tables may not be efficient. For instance, where jointcoding of chroma residuals is not enabled, it may not be necessary tosignal the joint Cb-Cr mapping table, as such a table will not be used.

As discussed in further details below, Chernyak et al., “AHG17/AHG15: Onquantization control parameters signaling,” Joint Video Experts Team,JVET-P0426, Geneva, CH, October 2019 (hereinafter “JVET-P0426”) proposedfor the signaling of the mapping tables to be based on the syntaxelement that indicates whether joint coding of chroma residuals isenabled or disabled for the one or more pictures of video data. Inparticular, JVET-P0426 allows for a video coder to avoid signaling thejoint Cb-Cr mapping table where joint coding of chroma residuals is notenabled.

However, the arrangement in JVET-P0426 may present one or moredisadvantages. In particular, as specified in JVET-P0426, the mappingtables are parsed from the bitstream before the syntax element thatindicates whether joint coding of chroma residuals is enabled ordisabled for the one or more pictures of video data. As such, thealleged ability to avoid signaling the joint Cb-Cr mapping table may notbe realized.

In accordance with one or more techniques of this disclosure, a videocoder may be configured to parse a syntax element that indicates whetherjoint coding of chroma residuals is enabled or disabled for the one ormore pictures of video data. As such, if the syntax element indicatesthat joint coding of chroma residuals is not enabled, the video codermay avoid signaling/parsing the joint Cb-Cr mapping table. In this way,the techniques of this disclosure may improve the coding efficiency ofvideo data (e.g., reduce the number of bits used to represent videodata).

As discussed above, a video coder may signal a syntax element in aparameter set a that indicates whether joint coding of chroma residualsis enabled or disabled for the one or more pictures of video datareferring to the parameter set. In addition, the video coder may signalone or more other syntax elements that specify various parameters forthe joint chroma coding mode (e.g., pps_joint_cbcr_qp_offset andjoint_cbcr_qp_offset_list[i]). For instance, the video coder may signala syntax element that specifies an offset to be applied to a luma QPwhen deriving a chroma QP. In some examples, the signalling of thesyntax element that specifies an offset to be applied to a luma QP whenderiving a chroma QP may be dependent on the value of the syntax elementthat indicates whether joint coding of chroma residuals is enabled ordisabled for the one or more pictures of video data.

The video coder may parse these syntax elements from a parameter setthat is different than the parameter set from which the syntax elementthat indicates whether joint coding of chroma residuals is enabled ordisabled for the one or more pictures of video data. For instance, thevideo coder may signal the syntax element that specifies an offset to beapplied to a luma QP when deriving a chroma QP in a picture parameterset (PPS) and signal the syntax element that indicates whether jointcoding of chroma residuals is enabled or disabled for the one or morepictures of video data in a sequence parameter set (SPS). However, onedesign principal of video coding may be to avoid parsing dependency.Coding the syntax element that specifies an offset to be applied to aluma QP when deriving a chroma QP in a PPS based on the value of thesyntax element that indicates whether joint coding of chroma residualsis enabled or disabled for the one or more pictures of video data in aSPS may violate this design principal.

In accordance with one or more techniques of this disclosure, as opposedto signaling syntax elements in the PPS that specify parameters for thejoint chroma coding mode as being dependent on the syntax element in theSPS that specifies whether the joint chroma coding mode is enabled, avideo coder may signal a syntax element in the PPS that specifieswhether the syntax elements that specify parameters for the joint chromacoding mode are present in the PPS (e.g.,pps_joint_cbcr_qp_offset_present_flag). While the value of the syntaxelement in the PPS that specifies whether the syntax elements thatspecify parameters for the joint chroma coding mode are present in thePPS may be at least semi redundant over the syntax element in the SPSthat that specifies whether the joint chroma coding mode is enabled,signaling this additional syntax element may eliminate the parameter setinterdependency, which may be desirable.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,unencoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1, system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, tablet computers, set-top boxes, telephone handsetssuch as smartphones, televisions, cameras, display devices, digitalmedia players, video gaming consoles, video streaming device, or thelike. In some cases, source device 102 and destination device 116 may beequipped for wireless communication, and thus may be referred to aswireless communication devices.

In the example of FIG. 1, source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques for quantizationparameter signaling for joint chroma residual mode. Thus, source device102 represents an example of a video encoding device, while destinationdevice 116 represents an example of a video decoding device. In otherexamples, a source device and a destination device may include othercomponents or arrangements. For example, source device 102 may receivevideo data from an external video source, such as an external camera.Likewise, destination device 116 may interface with an external displaydevice, rather than include an integrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniques forquantization parameter signaling for joint chroma residual mode. Sourcedevice 102 and destination device 116 are merely examples of such codingdevices in which source device 102 generates coded video data fortransmission to destination device 116. This disclosure refers to a“coding” device as a device that performs coding (encoding and/ordecoding) of data. Thus, video encoder 200 and video decoder 300represent examples of coding devices, in particular, a video encoder anda video decoder, respectively. In some examples, source device 102 anddestination device 116 may operate in a substantially symmetrical mannersuch that each of source device 102 and destination device 116 includesvideo encoding and decoding components. Hence, system 100 may supportone-way or two-way video transmission between source device 102 anddestination device 116, e.g., for video streaming, video playback, videobroadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e.,raw, unencoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some examples, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although memory 106 and memory 120 are shown separatelyfrom video encoder 200 and video decoder 300 in this example, it shouldbe understood that video encoder 200 and video decoder 300 may alsoinclude internal memories for functionally similar or equivalentpurposes. Furthermore, memories 106, 120 may store encoded video data,e.g., output from video encoder 200 and input to video decoder 300. Insome examples, portions of memories 106, 120 may be allocated as one ormore video buffers, e.g., to store raw, decoded, and/or encoded videodata.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may modulate a transmission signalincluding the encoded video data, and input interface 122 may demodulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video generated by source device 102. Destination device 116may access stored video data from file server 114 via streaming ordownload. File server 114 may be any type of server device capable ofstoring encoded video data and transmitting that encoded video data tothe destination device 116. File server 114 may represent a web server(e.g., for a website), a File Transfer Protocol (FTP) server, a contentdelivery network device, or a network attached storage (NAS) device.Destination device 116 may access encoded video data from file server114 through any standard data connection, including an Internetconnection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., digital subscriber line (DSL),cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on file server 114. File server 114and input interface 122 may be configured to operate according to astreaming transmission protocol, a download transmission protocol, or acombination thereof.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receivers, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., a communicationmedium, storage device 112, file server 114, or the like). The encodedvideo bitstream may include signaling information defined by videoencoder 200, which is also used by video decoder 300, such as syntaxelements having values that describe characteristics and/or processingof video blocks or other coded units (e.g., slices, pictures, groups ofpictures, sequences, or the like). Display device 118 displays decodedpictures of the decoded video data to a user. Display device 118 mayrepresent any of a variety of display devices such as a cathode ray tube(CRT), a liquid crystal display (LCD), a plasma display, an organiclight emitting diode (OLED) display, or another type of display device.

Although not shown in FIG. 1, in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual(MPEG-4 Part 2), ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC),including its Scalable Video Coding (SVC) and Multiview Video Coding(MVC) extensions and ITU-T H.265 (also known as ISO/IEC MPEG-4 HEVC)with its extensions. During the April 2018 meeting of the Joint VideoExperts Team (JVET), the Versatile Video Coding (VVC) standardizationactivity (also known as ITU-T H.266) was kicked off with the evaluationof the video compression technologies submitted to the Call forProposals.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Alternatively, videoencoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as the Joint Exploration TestModel (JEM) or ITU-T H.266, also referred to as Versatile Video Coding(VVC). A recent draft of the VVC standard is described in Bross, et al.“Versatile Video Coding (Draft 6),” Joint Video Experts Team (JVET) ofITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 15^(th) Meeting:Gothenburg, SE, 3-12 Jul. 2019, JVET-02001-v14 (hereinafter “VVC Draft6”). The techniques of this disclosure, however, are not limited to anyparticular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to JEM or VVC. According to JEM or VVC,a video coder (such as video encoder 200) partitions a picture into aplurality of coding tree units (CTUs). Video encoder 200 may partition aCTU according to a tree structure, such as a quadtree-binary tree (QTBT)structure or Multi-Type Tree (MTT) structure. The QTBT structure removesthe concepts of multiple partition types, such as the separation betweenCUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a firstlevel partitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using aquadtree (QT) partition, a binary tree (BT) partition, and one or moretypes of triple tree (TT) (also called ternary tree (TT)) partitions. Atriple or ternary tree partition is a partition where a block is splitinto three sub-blocks. In some examples, a triple or ternary treepartition divides a block into three sub-blocks without dividing theoriginal block through the center. The partitioning types in MTT (e.g.,QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT or MTT structure to represent each of the luminance andchrominance components, while in other examples, video encoder 200 andvideo decoder 300 may use two or more QTBT or MTT structures, such asone QTBT/MTT structure for the luminance component and another QTBT/MTTstructure for both chrominance components (or two QTBT/MTT structuresfor respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning, MTT partitioning, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

The blocks (e.g., CTUs or CUs) may be grouped in various ways in apicture. As one example, a brick may refer to a rectangular region ofCTU rows within a particular tile in a picture. A tile may be arectangular region of CTUs within a particular tile column and aparticular tile row in a picture. A tile column refers to a rectangularregion of CTUs having a height equal to the height of the picture and awidth specified by syntax elements (e.g., such as in a picture parameterset). A tile row refers to a rectangular region of CTUs having a heightspecified by syntax elements (e.g., such as in a picture parameter set)and a width equal to the width of the picture.

In some examples, a tile may be partitioned into multiple bricks, eachof which may include one or more CTU rows within the tile. A tile thatis not partitioned into multiple bricks may also be referred to as abrick. However, a brick that is a true subset of a tile may not bereferred to as a tile.

The bricks in a picture may also be arranged in a slice. A slice may bean integer number of bricks of a picture that may be exclusivelycontained in a single network abstraction layer (NAL) unit. In someexamples, a slice includes either a number of complete tiles or only aconsecutive sequence of complete bricks of one tile.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

Some examples of JEM and VVC also provide an affine motion compensationmode, which may be considered an inter-prediction mode. In affine motioncompensation mode, video encoder 200 may determine two or more motionvectors that represent non-translational motion, such as zoom in or out,rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. Some examples ofJEM and VVC provide sixty-seven intra-prediction modes, includingvarious directional modes, as well as planar mode and DC mode. Ingeneral, video encoder 200 selects an intra-prediction mode thatdescribes neighboring samples to a current block (e.g., a block of a CU)from which to predict samples of the current block. Such samples maygenerally be above, above and to the left, or to the left of the currentblock in the same picture as the current block, assuming video encoder200 codes CTUs and CUs in raster scan order (left to right, top tobottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT),an integer transform, a wavelet transform, or a conceptually similartransform to residual video data. Additionally, video encoder 200 mayapply a secondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the transform coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of the transformcoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) transform coefficients at the front of the vector and toplace lower energy (and therefore higher frequency) transformcoefficients at the back of the vector. In some examples, video encoder200 may utilize a predefined scan order to scan the quantized transformcoefficients to produce a serialized vector, and then entropy encode thequantized transform coefficients of the vector. In other examples, videoencoder 200 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form the one-dimensional vector, video encoder200 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information of apicture into CTUs, and partitioning of each CTU according to acorresponding partition structure, such as a QTBT structure, to defineCUs of the CTU. The syntax elements may further define prediction andresidual information for blocks (e.g., CUs) of video data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

VVC Draft 6 supports a mode where the chroma residuals are codedjointly. The usage (activation) of a joint chroma coding mode isindicated by a TU-level flag tu_joint_cbcr_residual_flag and theselected mode is implicitly indicated by the chroma CBFs. The flagtu_joint_cbcr_residual_flag is present if either or both chroma CBFs fora TU are equal to 1. In the PPS and slice header, chroma QP offsetvalues are signalled for the joint chroma residual coding mode todifferentiate from the usual chroma QP offset values signalled forregular chroma residual coding mode. These chroma QP offset values areused to derive the chroma QP values for those blocks coded using thejoint chroma residual coding mode. When a corresponding joint chromacoding mode (modes 2 in Table 3-12) is active in a TU, this chroma QPoffset is added to the applied luma-derived chroma QP duringquantization and decoding of that TU. For the other modes (modes 1 and 3in Table 3-12), the chroma QPs may be derived in the same way as forconventional Cb or Cr blocks. The reconstruction process of the chromaresiduals (resCb and resCr) from the transmitted transform blocks isdepicted in Table 3-12. When this mode is activated, one single jointchroma residual block (resJointC[x][y] in Table 3-12) may be signalled,and a residual block for Cb (resCb) and residual block for Cr (resCr)are derived considering information such as tu_cbf_cb, tu_cbf_cr, andCSign, which is a sign value specified in the slice header. Examples ofsuch techniques may be found in Helmrich et al. “Joint chroma residualcoding with multiple modes (tests CE7-2.1, CE7-2.2)”, Document of JointVideo Experts Team, JVET-00105, Gothenburg, SE, July 2019 and Helmrichet al. “Alternative configuration for joint chroma residual coding”,Document of Joint Video Experts Team, JVET-00543, Gothenburg, SE, July2019.

At the encoder side, the joint chroma components may be derived asexplained in the following. Depending on the mode (listed in the tablesabove), resJointC{1,2} may be generated by the encoder as follows:

-   -   If mode is equal to 2 (single residual with reconstruction Cb=C,        Cr=CSign*C), the joint residual is determined according to

resJointC[x][y]=(resCb[x][y]+CSign*resCr[x][y])/2.

-   -   Otherwise, if mode is equal to 1 (single residual with        reconstruction Cb=C, Cr=(CSign*C)/2), the joint residual is        determined according to

resJointC[x][y]=(4*resCb[x][y]+2*CSign*resCr[x][y])/5.

-   -   Otherwise (mode is equal to 3, i. e., single residual,        reconstruction Cr=C, Cb=(CSign*C)/2), the joint residual is        determined according to

resJointC[x][y]=(4*resCr[x][y]+2*CSign*resCb[x][y])/5.

Table 3-12 Reconstruction of chroma residuals. The value CSign is a signvalue (+1 or −1), which is specified in the slice header, resJointC[f]is the transmitted residual.

tu_cbf_cb tu_cbf_cr reconstruction of Cb and Cr residuals mode 1 0resCb[ x ][ y ] = resJointC[ x ][ y ] 1 resCr[ x ][ y ] = ( CSign *resJointC[ x ][ y ] ) >> 1 1 1 resCb[ x ][ y ] = resJointC[ x ][ y ] 2resCr[ x ][ y ] = CSign * resJointC[ x ][ y ] 0 1 resCb[ x ][ y ] = (CSign * resJointC[ x ][ y ] ) >> 1 3 resCr[ x ][ y ] = resJointC[ x ][ y]

The three joint chroma coding modes described above are only supportedin I slices. In P and B slices, only mode 2 may be supported. Hence, inP and B slices, the syntax element tu_joint_cbcr_residual_flag is onlypresent if both chroma cbfs are 1. Note that transform depth is removedin the context modeling of tu_cbf_luma and tu_cbf_cb.

In Yang et al., “Non-CE6: Refined LFNST restriction with MIP,” JointVideo Experts Team, JVET-P0376, Geneva, CH, October 2019 (see also Xu etal. “CE8-related: A SPS Level Flag for BDPCM and JCCR”, Document ofJoint Video Experts Team, JVET-00376, Gothenburg, SE, July 2019), asequence parameter set (SPS) level flag has been added to controlenabling/disabling of joint-Cb-Cr for each video sequence (see alsoRamasubramonian et al. “AHG15: On signalling of chroma QP tables”,Document of Joint Video Experts Team, JVET-00543, Gothenburg, SE, July2019). VVC Draft 6 incorporates these techniques and the correspondingflag is referred to as sps_joint_cbcr_enabled_flag.

In Ramasubramonian et al., “AHG15: On signalling of chroma QP tables,”Joint Video Experts Team, JVET-00650, Gothenburg, SE, July 2019(hereinafter “JVET-00650”), a SPS level signaling of chroma QP mappingtables, for the derivation of chroma QP from thecollocated/corresponding luma block QP, is proposed. JVET-00650 providesflexibility to use different table for Cb, Cr, and joint-Cb-Cr, and toadapt the table based on the nature of the video content(SDR/HDR-PQ/HDR-HLG).

The aforementioned techniques may present one or more disadvantages. Inparticular, in VVC Draft 6, when sps_joint_cbcr_enabled_flag is 0, thefollowing occurs:

-   -   1. Chroma QP mapping tables—delta_qp_in_val_minus1[i][j] and        delta_qp_out_val[i][j]—are still signalled for joint-Cb-Cr.    -   2. Also, at the picture parameter set (PPS) level        pps_joint_cbcr_qp_offset and joint_cbcr_qp_offset_list[i] are        signalled.

This signaling may be redundant, which may unnecessarily decrease thecoding efficiency (e.g., increase the number of bits used to representvideo data at a particular quality). Relevant portions of VVC Draft arereproduced below:

sps_max_luma_transform_size_64 flag u(1) if( ChromaArrayType != 0 ) {same_qp_table_for_chroma u(1) for(i = 0; i < same_qp_table_for_chroma ?1 : 3; i++ ) { num_points_in_qp_table_minus1 [ i ] ue(v) for(j = 0; j <=num_points_in_qp_table_minus1[ i ]; j++ ) { (delta_qp_in_val_minus1[ i][ j ] ue(v) delta_qp_out_val[ i ][ j ] ue(v) } } }sps_weighted_pred_flag u(1) sps_weighted_bipred_flag u(1)sps_sao_enabled_flag u(1) sps_alf_enabled_flag u(1)sps_transform_skip_enabled_flag u(1) if(sps_transform_skip_enabled_flag) sps_bdpcm_enabled_flag u(1)sps_joint_cbcr_enabled_flag u(1) sps_ref_wrap_around_enabled_flag u(1)if( sps_ref_wraparound_enabled_flag) sps_ref_wraparound_offset_minus1ue(v) pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)pps_joint_cbcr_qp_offset se(v) pps_slice_chroma_qp_offsets_present_flagu(1) cu_chroma_qp_offset_enabled_flag u(1) if(cu_chroma_qp_offset_enabled_flag) { cu_chroma_qp_offset_subdiv ue(v)chroma_qp_offset_list_len_minus1 ue(v) for( i = 0; i <=chroma_qp_offset_list_len_minus1; i++ ) { eb_qp_offset_list[ i ] se(v)cr_qp_offset_list[ i ] se(v) joint_cbcr_qp_offset_list[ i ] se(v) } }

In aspect 1 of Chernyak et al., “AHG17/AHG15: On quantization controlparameters signaling,” Joint Video Experts Team, JVET-P0426, Geneva, CH,October 2019 (hereinafter “JVET-P0426”), it was proposed to usesps_joint_cbcr_enabled_flag for the parsing of chroma QP mapping tableand, pps level qp offset parameters, as shown the modification inspecification text in JVET-P0426, shown below.

Descriptor seq_parameter_set_rbsp( ) { . . . if( ChromaArrayType != 0 ){ same_qp_table_for_chroma u(1) for( i = 0; i < same_qp_table_for_chroma? 1 :

(sps_joint_cbcr_enabled_flag ? 3 : 2); i++ ) {num_points_in_qp_table_minus1[ i ] ue(v) for( j = 0; j <=num_points_in_qp_table_minus1[ i ]; j++){ delta_qp_in_val_minus1[ i ][ j] ue(v) delta_qp_out_val[ i ][ j ] ue(v) } } } . . . }pic_parameter_set_rbsp( ) { . . . pps_cb_qp_offset se(v)pps_cr_qp_offset se(v) if( sps_joint_cbcr_enabled_flag)pps_joint_cbcr_qp_offset se(v) pps_slice_chroma_qp_offsets_present_flagu(1) cu_chroma_qp_offset_enabled_flag u(1) if(cu_chroma_qp_offset_enabled_flag) { cu_chroma_qp_offset_subdiv ue(v)chroma_qp_offset_list_len_minus1 ue(v) for( i = 0; i <=chroma_qp_offset_list_len_minus1; i++ ) { cb_qp_offset_list[ i ] se(v)cr_qp_offset_list[ i ] se(v) if( sps_joint_cbcr_enabled_flag)joint_cbcr_qp_offset_list[ i ] se(v) } } . . . }

The solution proposed in aspect 1 of JVET-P0426 may present one or moredisadvantages. Two specific disadvantages are discussed as follows. As afirst disadvantage, currently, at the SPS level,sps_joint_cbcr_enabled_flag is parsed after the parsing of chroma QPmapping table(s). As such, the desired outcome of the proposed aspect(removing chroma QP mapping table for JCCR) may not be achieved unlessthe parsing order is modified. As a second disadvantage, at the PPSlevel, parsing of PPS syntax elements pps_joint_cbcr_qp_offset andjoint_cbcr_qp_offset_list[i] depends on the SPS syntax elementsps_joint_cbcr_enabled_flag. However, one of the design principles ofVVC is to avoid parameter set parsing dependency. In this case, PPSparameters depend on SPS parameter which violates this design principle.

This disclosure proposes several techniques that may cure thedisadvantages discussed above and/or provide other advantages. Thetechniques of disclosure may include two aspects, which may be usedindependently or in combination. In accordance with a first aspect ofthis disclosure, a video coder (e.g., video encoder 200 and/or videodecoder 300) may code (e.g., encoder or parse) a syntax element thatindicates whether the joint coding of chroma residuals is enabled ordisabled (e.g., sps_joint_cbcr_enabled_flag) before parsing of thechroma QP mapping table. For instance, the syntax table may be modifiedto adjust the parsing order of sps_joint_cbcr_enabled_flag.

In accordance with a second aspect of this disclosure, the video codermay code a syntax element (e.g., pps_joint_cbcr_qp_offset_present_flag)to control whether the QP offset for the joint Cb-Cr residuals isincluded in the chroma QP offset table and whether a syntax element thatspecifies the offset to the luma quantization parameter Qp′_(Y) used forderiving Qp′_(CbCr) (e.g., pps_joint_cbcr_qp_offset) is coded. Asopposed to the approach of JVET-P0426, this approach does not have anyparsing dependency.

Example changes compared to VVC Draft 6 are marked below in italics:

sps_max_luma_transform_size_64_flag u(1) sps_joint_cbcr_enabled_flagu(1) if( ChromaArrayType != 0 ) { same_qp_table_for_chroma u(1) for( i =0; i < same_qp_table_for_chroma ? 1 : (sps_joint_cbcr_enabled_flag)? 3:2 ; i+ + ) { num_points_in_qp_table_minus1[ i ] ue(v) for( j = 0; j <=num_points_in_qp_table_minus1 [ i ]; j++ ) { delta_qp_in_val_minus1[ i][ j ] ue(v) delta_qp_out_val[ i ][ j ] ue(v) } } }sps_weighted_pred_flag u(1) sps_weighted_bipred_flag u(1)sps_sao_enabled_flag u(1) sps_alf_enabled_flag u(1)sps_transform_skip_enabled_flag u(1) if(sps_transform_skip_enabled_flag) sps_bdpcm_enabled_flag u(1)pps_cb_qp_offset se(v) pps_cr_qp_offset se(v)pps_joint_cbcr_qp_offset_present_flag u(1)if(pps_joint_cbcr_qp_offset_present_flag) pps_joint_cbcr_qp_offset se(v)pps_slice_chroma_qp_offsets_present_flag u(1)cu_chroma_qp_offset_enabled_flag u(1) if(cu_chroma_qp_offset_enabled_flag) { cu_chroma_qp_offset_subdiv ue(v)chroma_qp_offset_list_len_minus1 ue(v) for( i = 0; i <=chroma_qp_offset_list_len_minus1; i++ ) { cb_qp_offset_list[ i ] se(v)cr_qp_offset_list[ i ] se(v) if(pps_joint_cbcr_qp_offset_present_flag)joint_cbcr_qp_offset_list[ i ] se(v) } }pps_joint_cbcr_qp_offset_present_flag equal to 1 specifies thatpps_joint_cbcr_qp_offset and joint_cbcr_qp_offset_list[i] are present inthe PPS RBSP syntax structure. pps_joint_cbcr_qp_offset_present_flagequal to 0 specifies that pps_joint_cbcr_qp_offset andjoint_cbcr_qp_offset_list[i] are not present in the PPS RBSP syntaxstructure. When ChromaArrayType is equal to 0 orsps_joint_cbcr_enabled_flag is equal to 0, the value ofpps_joint_cbcr_qp_offset_present_flag shall be equal to 0.pps_joint_cbcr_qp_offset specifies the offset to the luma quantizationparameter Qp′_(Y) used for deriving Qp′_(CbCr). The value ofpps_joint_cbcr_qp_offset shall be in the range of −12 to +12, inclusive.When pps_joint_cbcr_qp_offset_present_flag is equal to 0,pps_joint_cbcr_qp_offset is not present and is inferred to be equal to0.cb_qp_offset_list[i], cr_qp_offset_list[i], andjoint_cbcr_qp_offset_list[i], specify offsets used in the derivation ofQp′_(Cb), Qp′_(Cr), and Qp′_(CbCr), respectively. The values ofcb_qp_offset_list[i], cr_qp_offset_list[i], andjoint_cbcr_qp_offset_list[i] shall be in the range of −12 to +12,inclusive. When pps_joint_cbcr_qp_offset_present_flag is equal to 0,joint_cbcr_qp_offset_list[i] is not present and is inferred to be equalto 0.

In accordance with the techniques of this disclosure, a video coder maycode a sequence parameter set (SPS) referred to by one or more picturesof video data, wherein, to code the SPS, the video coder may: code, at afirst position in the SPS, a syntax element that indicates whether jointcoding of chroma residuals is enabled or disabled for the one or morepictures of video data referring to the SPS; and code, at a secondposition in the SPS that is after the first position, one or more syntaxelements representing a quantization parameter (QP) mapping table; codea picture parameter set (PPS) referred to by a picture of the one ormore pictures of video data, wherein, to code the PPS, the video codermay code a syntax element that indicates whether a QP offset for thejoint chroma residuals is included in the chroma QP offset table andwhether a syntax element that specifies an offset to the lumaquantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) is coded;and code the picture based on the SPS and the PPS.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure 130, and a corresponding coding tree unit(CTU) 132. The solid lines represent quadtree splitting, and dottedlines indicate binary tree splitting. In each split (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting in this example.For the quadtree splitting, there is no need to indicate the splittingtype, because quadtree nodes split a block horizontally and verticallyinto 4 sub-blocks with equal size. Accordingly, video encoder 200 mayencode, and video decoder 300 may decode, syntax elements (such assplitting information) for a region tree level of QTBT structure 130(i.e., the solid lines) and syntax elements (such as splittinginformation) for a prediction tree level of QTBT structure 130 (i.e.,the dashed lines). Video encoder 200 may encode, and video decoder 300may decode, video data, such as prediction and transform data, for CUsrepresented by terminal leaf nodes of QTBT structure 130.

In general, CTU 132 of FIG. 2B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), then the nodes can befurther partitioned by respective binary trees. The binary treesplitting of one node can be iterated until the nodes resulting from thesplit reach the minimum allowed binary tree leaf node size (MinBTSize)or the maximum allowed binary tree depth (MaxBTDepth). The example ofQTBT structure 130 represents such nodes as having dashed lines forbranches. The binary tree leaf node is referred to as a coding unit(CU), which is used for prediction (e.g., intra-picture or inter-pictureprediction) and transform, without any further partitioning. Asdiscussed above, CUs may also be referred to as “video blocks” or“blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If theleaf quadtree node is 128×128, the leaf quadtree node will not befurther split by the binary tree, because the size exceeds the MaxBTSize(i.e., 64×64, in this example). Otherwise, the leaf quadtree node willbe further partitioned by the binary tree. Therefore, the quadtree leafnode is also the root node for the binary tree and has the binary treedepth as 0. When the binary tree depth reaches MaxBTDepth (4, in thisexample), no further splitting is permitted. When the binary tree nodehas a width equal to MinBTSize (4, in this example), it implies nofurther horizontal splitting is permitted. Similarly, a binary tree nodehaving a height equal to MinBTSize implies no further vertical splittingis permitted for that binary tree node. As noted above, leaf nodes ofthe binary tree are referred to as CUs, and are further processedaccording to prediction and transform without further partitioning.

FIG. 3 is a block diagram illustrating an example video encoder 200 thatmay perform the techniques of this disclosure. FIG. 3 is provided forpurposes of explanation and should not be considered limiting of thetechniques as broadly exemplified and described in this disclosure. Forpurposes of explanation, this disclosure describes video encoder 200 inthe context of video coding standards such as the HEVC video codingstandard and the H.266 video coding standard in development. However,the techniques of this disclosure are not limited to these video codingstandards, and are applicable generally to video encoding and decoding.

In the example of FIG. 3, video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videoencoder 200 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video encoder 200 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 3 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, one or more of the units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1) may store theinstructions (e.g., object code) of the software that video encoder 200receives and executes, or another memory within video encoder 200 (notshown) may store such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,unencoded version of the current block from video data memory 230 andthe prediction block from mode selection unit 202. Residual generationunit 204 calculates sample-by-sample differences between the currentblock and the prediction block. The resulting sample-by-sampledifferences define a residual block for the current block. In someexamples, residual generation unit 204 may also determine differencesbetween sample values in the residual block to generate a residual blockusing residual differential pulse code modulation (RDPCM). In someexamples, residual generation unit 204 may be formed using one or moresubtractor circuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder200 and video decoder 300 may also support asymmetric partitioning forPU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit 202 does not further partition aCU into PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as fewexamples, mode selection unit 202, via respective units associated withthe coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the transform coefficient blocksassociated with the current block by adjusting the QP value associatedwith the CU. Quantization may introduce loss of information, and thus,quantized transform coefficients may have lower precision than theoriginal transform coefficients produced by transform processing unit206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from theprediction block generated by mode selection unit 202 to produce thereconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not needed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are needed, filter unit 216may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying a MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding block andthe chroma coding blocks.

Video encoder 200 represents an example of a device configured to encodevideo data including a memory configured to store video data, and one ormore processing units implemented in circuitry and configured to encodea sequence parameter set (SPS) referred to by one or more pictures ofvideo data, wherein, to encode the SPS, the video encoder may: encode,at a first position in the SPS, a syntax element that indicates whetherjoint coding of chroma residuals is enabled or disabled for the one ormore pictures of video data referring to the SPS; and encode, at asecond position in the SPS that is after the first position, one or moresyntax elements representing a quantization parameter (QP) mappingtable; encode a picture parameter set (PPS) referred to by a picture ofthe one or more pictures of video data, wherein, to encode the PPS, thevideo encoder may encode a syntax element that indicates whether a QPoffset for the joint chroma residuals is included in the chroma QPoffset table and whether a syntax element that specifies an offset tothe luma quantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) isencoded; and encode the picture based on the SPS and the PPS.

FIG. 4 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 4 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 according tothe techniques of JEM, VVC, and HEVC. However, the techniques of thisdisclosure may be performed by video coding devices that are configuredto other video coding standards.

In the example of FIG. 4, video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videodecoder 300 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video decoder 300 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeadditional units to perform prediction in accordance with otherprediction modes. As examples, prediction processing unit 304 mayinclude a palette unit, an intra-block copy unit (which may form part ofmotion compensation unit 316), an affine unit, a linear model (LM) unit,or the like. In other examples, video decoder 300 may include more,fewer, or different functional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as DRAM, including SDRAM, MRAM,RRAM, or other types of memory devices. CPB memory 320 and DPB 314 maybe provided by the same memory device or separate memory devices. Invarious examples, CPB memory 320 may be on-chip with other components ofvideo decoder 300, or off-chip relative to those components.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 4 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 3, fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, one or moreof the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, one or more of the units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the transform coefficient block.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 3).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 3).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Forinstance, in examples where operations of filter unit 312 are notperformed, reconstruction unit 310 may store reconstructed blocks to DPB314. In examples where operations of filter unit 312 are performed,filter unit 312 may store the filtered reconstructed blocks to DPB 314.As discussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures (e.g.,decoded video) from DPB 314 for subsequent presentation on a displaydevice, such as display device 118 of FIG. 1.

In this manner, video decoder 300 represents an example of a videodecoding device including a memory configured to store video data, andone or more processing units implemented in circuitry and configured todecode a sequence parameter set (SPS) referred to by one or morepictures of video data, wherein, to decode the SPS, the video decodermay: decode, at a first position in the SPS, a syntax element thatindicates whether joint coding of chroma residuals is enabled ordisabled for the one or more pictures of video data referring to theSPS; and decode, at a second position in the SPS that is after the firstposition, one or more syntax elements representing a quantizationparameter (QP) mapping table; decode a picture parameter set (PPS)referred to by a picture of the one or more pictures of video data,wherein, to decode the PPS, the video decoder may decode a syntaxelement that indicates whether a QP offset for the joint chromaresiduals is included in the chroma QP offset table and whether a syntaxelement that specifies an offset to the luma quantization parameterQp′_(Y) used for deriving Qp′_(CbCr) is signalled; and decode thepicture based on the SPS and the PPS.

FIG. 5 is a flowchart illustrating an example method for encoding acurrent block. The current block may comprise a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 3), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 5.

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. Video encoder 200 may then calculate a residual blockfor the current block (352). To calculate the residual block, videoencoder 200 may calculate a difference between the original, unencodedblock and the prediction block for the current block. Video encoder 200may then transform and quantize coefficients of the residual block(354). Next, video encoder 200 may scan the quantized transformcoefficients of the residual block (356). During the scan, or followingthe scan, video encoder 200 may entropy encode the transformcoefficients (358). For example, video encoder 200 may encode thetransform coefficients using CAVLC or CABAC. Video encoder 200 may thenoutput the entropy encoded data of the block (360).

FIG. 6 is a flowchart illustrating an example method for decoding acurrent block of video data. The current block may comprise a currentCU. Although described with respect to video decoder 300 (FIGS. 1 and4), it should be understood that other devices may be configured toperform a method similar to that of FIG. 6.

Video decoder 300 may receive entropy encoded data for the currentblock, such as entropy encoded prediction information and entropyencoded data for coefficients of a residual block corresponding to thecurrent block (370). Video decoder 300 may entropy decode the entropyencoded data to determine prediction information for the current blockand to reproduce coefficients of the residual block (372). Video decoder300 may predict the current block (374), e.g., using an intra- orinter-prediction mode as indicated by the prediction information for thecurrent block, to calculate a prediction block for the current block.Video decoder 300 may then inverse scan the reproduced coefficients(376), to create a block of quantized transform coefficients. Videodecoder 300 may then inverse quantize and inverse transform thetransform coefficients to produce a residual block (378). Video decoder300 may ultimately decode the current block by combining the predictionblock and the residual block (380).

FIG. 7 is a flowchart illustrating an example method for coding acurrent block of video data. The current block may comprise a currentCU. Although described with respect to video decoder 300 (FIGS. 1 and4), it should be understood that other devices may be configured toperform a method similar to that of FIG. 7.

Video decoder 300 may decode, from an encoded video bitstream, asequence parameter set (SPS) referred to by one or more pictures ofvideo data. For instance, entropy decoding unit 302 may parse, at afirst position in the SPS, a syntax element that indicates whether jointcoding of chroma residuals is enabled or disabled for the one or morepictures of video data referring to the SPS (702); and parse, at asecond position in the SPS that is after the first position, one or moresyntax elements representing quantization parameter (QP) mapping tables(704). In some examples, the syntax element that indicates whether jointcoding of chroma residuals is enabled or disabled for the one or morepictures of video data referring to the SPS may include asps_joint_cbcr_enabled_flag syntax element. In some examples, the one ormore syntax elements representing a quantization parameter (QP) mappingtable may include one or more num_points_in_qp_table_minus1[i] syntaxelements, one or more delta_qp_in_val_minus1[i][j] syntax elements, andone or more delta_qp_out_val[I][j] syntax elements. As discussed above,by parsing the a syntax element that indicates whether joint coding ofchroma residuals is enabled or disabled for the one or more pictures ofvideo data referring to the SPS before the one or more syntax elementsrepresenting quantization parameter (QP) mapping tables, video decoder300 may avoid decoding syntax elements representing quantizationparameter (QP) mapping tables for joint Cb-Cr mapping table where jointcoding of chroma residuals is disabled.

Video decoder 300 may decode, from the encoded video bitstream, apicture parameter set (PPS) referred to by a picture of the one or morepictures of video data. For instance, entropy decoding unit 302 mayparse, from the PPS, a syntax element that indicates whether syntaxelements related to joint coding of chroma residuals are present in thePPS (706). The syntax element that indicates whether syntax elementsrelated to joint coding of chroma residuals are present in the PPS maybe a syntax element that indicates whether a QP offset for jointly codedchroma residuals is included in a chroma QP offset table and whether asyntax element that specifies an offset to a luma quantization parameterQp′_(Y) used for deriving Qp′_(CbCr) is coded. In some examples, thesyntax element that indicates whether a QP offset for the jointly codedchroma residuals is included in the chroma QP offset table and whetherthe syntax element that specifies the offset to the luma quantizationparameter Qp′_(Y) used for deriving Qp′_(CbCr) is coded may be apps_joint_cbcr_qp_offset_present_flag syntax element.

In some examples, to decode the PPS, entropy decoding unit 302 may parsethe syntax elements related to joint coding of chroma residuals based onthe value of the parsed syntax element (e.g., based on a value ofpps_joint_cbcr_qp_offset_present_flag). For instance,pps_joint_cbcr_qp_offset_present_flag indicates thatpps_joint_cbcr_qp_offset and joint_cbcr_qp_offset_list[i] are present,entropy decoding unit 302 may parse, from the PPS, thepps_joint_cbcr_qp_offset and joint_cbcr_qp_offset_list[i] syntaxelements.

Video decoder 300 may decode the picture based on the SPS and the PPS(708). For instance, entropy decoding unit 302 may selectively performjoint chroma residual coding based on values of the syntax elements ofthe SPS and PPS. In some examples, to decode the picture based on theSPS and the PPS, video decoder 300 may decode the picture based on theQP mapping table specified by the SPS.

The following numbered examples may illustrate one or more aspects ofthe disclosure:

Example 1. A method of coding video data, the method comprising: codinga sequence parameter set (SPS) referred to by one or more pictures ofvideo data, wherein coding the SPS comprises: coding, at a firstposition in the SPS, a syntax element that indicates whether jointcoding of chroma residuals is enabled or disabled for the one or morepictures of video data referring to the SPS; and coding, at a secondposition in the SPS that is after the first position, one or more syntaxelements representing a quantization parameter (QP) mapping table;coding a picture parameter set (PPS) referred to by a picture of the oneor more pictures of video data, wherein coding the PPS comprises: codinga syntax element that indicates whether a QP offset for jointly codedchroma residuals is included in a chroma QP offset table and whether asyntax element that specifies an offset to a luma quantization parameterQp′_(Y) used for deriving Qp′_(CbCr) is coded; and coding the picturebased on the SPS and the PPS.

Example 2. The method of example 1, wherein the syntax element thatindicates whether joint coding of chroma residuals is enabled ordisabled for the one or more pictures of video data referring to the SPScomprises a sps_joint_cbcr_enabled_flag syntax element.

Example 3. The method of example 1 or example 2, wherein the syntaxelement that indicates whether a QP offset for the jointly coded chromaresiduals is included in the chroma QP offset table and whether thesyntax element that specifies the offset to the luma quantizationparameter Qp′_(Y) used for deriving Qp′_(CbCr) is coded comprises apps_joint_cbcr_qp_offset_present_flag syntax element.

Example 4. The method of any of examples 1-3, wherein the syntax elementthat specifies the offset to the luma quantization parameter Qp′_(Y)used for deriving Qp′_(CbCr) comprises a pps_joint_cbcr_qp_offset syntaxelement.

Example 5. The method of any of examples 1-4, wherein coding comprisesdecoding.

Example 6. The method of any of examples 1-5, wherein coding comprisesencoding.

Example 7. A device for coding video data, the device comprising one ormore means for performing the method of any of examples 1-6.

Example 8. The device of example 7, wherein the one or more meanscomprise one or more processors implemented in circuitry.

Example 9. The device of any of examples 7 and 8, further comprising amemory to store the video data.

Example 10. The device of any of examples 7-9, further comprising adisplay configured to display decoded video data.

Example 11. The device of any of examples 7-10, wherein the devicecomprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.

Example 12. The device of any of examples 7-11, wherein the devicecomprises a video decoder.

Example 13. The device of any of examples 7-12, wherein the devicecomprises a video encoder.

Example 14. A computer-readable storage medium having stored thereoninstructions that, when executed, cause one or more processors toperform the method of any of examples 1-6.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the terms “processor” and “processingcircuitry,” as used herein may refer to any of the foregoing structuresor any other structure suitable for implementation of the techniquesdescribed herein. In addition, in some aspects, the functionalitydescribed herein may be provided within dedicated hardware and/orsoftware modules configured for encoding and decoding, or incorporatedin a combined codec. Also, the techniques could be fully implemented inone or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of decoding video data, the methodcomprising: decoding, from an encoded video bitstream, a sequenceparameter set (SPS) referred to by one or more pictures of video data,wherein decoding the SPS comprises: parsing, at a first position in theSPS, a syntax element that indicates whether joint coding of chromaresiduals is enabled or disabled for the one or more pictures of thevideo data referring to the SPS; and parsing, at a second position inthe SPS that is after the first position, one or more syntax elementsrepresenting a quantization parameter (QP) mapping table; decoding, fromthe encoded video bitstream, a picture parameter set (PPS) referred toby a picture of the one or more pictures of video data, wherein decodingthe PPS comprises: parsing a syntax element that indicates whether a QPoffset for jointly coded chroma residuals is included in a chroma QPoffset table and whether a syntax element that specifies an offset to aluma quantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) iscoded; and decoding the picture based on the SPS and the PPS.
 2. Themethod of claim 1, wherein the syntax element that indicates whetherjoint coding of chroma residuals is enabled or disabled for the one ormore pictures of video data referring to the SPS comprises asps_joint_cbcr_enabled_flag syntax element.
 3. The method of claim 1,wherein the syntax element that indicates whether a QP offset for thejointly coded chroma residuals is included in the chroma QP offset tableand whether the syntax element that specifies the offset to the lumaquantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) is codedcomprises a pps_joint_cbcr_qp_offset_present_flag syntax element.
 4. Themethod of claim 1, wherein decoding the PPS further comprises: parsing,based on a value of the syntax element that indicates whether a QPoffset for jointly coded chroma residuals is included in a chroma QPoffset table and whether a syntax element that specifies an offset to aluma quantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) iscoded: a syntax element that indicates whether the QP offset for jointlycoded chroma residuals is included in a chroma QP offset table; and thesyntax element that specifies whether the offset to the lumaquantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) is coded. 5.The method of claim 1, further comprising: parsing, based on the syntaxelement that indicates whether the QP offset for jointly coded chromaresiduals is included in the chroma QP offset table and whether thesyntax element that specifies an offset to the luma quantizationparameter Qp′_(Y) used for deriving Qp′_(CbCr) is coded, the syntaxelement that specifies the offset to the luma quantization parameterQp′_(Y) used for deriving Qp′_(CbCr), wherein the syntax element thatspecifies the offset to the luma quantization parameter Qp′_(Y) used forderiving Qp′_(CbCr) comprises a pps_joint_cbcr_qp_offset syntax element.6. A device for decoding video data, the device comprising a memoryconfigured to store at least a portion of an encoded video bitstream;and one or more processors that are implemented in circuitry andconfigured to: decode, from the encoded video bitstream, a sequenceparameter set (SPS) referred to by one or more pictures of video data,wherein, to decode the SPS, the one or more processors are configuredto: parse, at a first position in the SPS, a syntax element thatindicates whether joint coding of chroma residuals is enabled ordisabled for the one or more pictures of video data referring to theSPS; and parse, at a second position in the SPS that is after the firstposition, one or more syntax elements representing a quantizationparameter (QP) mapping table; decode, from the encoded video bitstream,a picture parameter set (PPS) referred to by a picture of the one ormore pictures of video data, wherein, to decode the PPS, the one or moreprocessors are configured to: parse a syntax element that indicateswhether a QP offset for jointly coded chroma residuals is included in achroma QP offset table and whether a syntax element that specifies anoffset to a luma quantization parameter Qp′_(Y) used for derivingQp′_(CbCr) is coded; and decode the picture based on the SPS and thePPS.
 7. The device of claim 6, wherein the syntax element that indicateswhether joint coding of chroma residuals is enabled or disabled for theone or more pictures of video data referring to the SPS comprises asps_joint_cbcr_enabled_flag syntax element.
 8. The device of claim 6,wherein the syntax element that indicates whether a QP offset for thejointly coded chroma residuals is included in the chroma QP offset tableand whether the syntax element that specifies the offset to the lumaquantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) is codedcomprises a pps_joint_cbcr_qp_offset_present_flag syntax element.
 9. Thedevice of claim 6, wherein, to decode the PPS, the one or moreprocessors are configured to: parse, based on a value of the syntaxelement that indicates whether a QP offset for jointly coded chromaresiduals is included in a chroma QP offset table and whether a syntaxelement that specifies an offset to a luma quantization parameterQp′_(Y) used for deriving Qp′_(CbCr) is coded: a syntax element thatindicates whether the QP offset for jointly coded chroma residuals isincluded in a chroma QP offset table; and the syntax element thatspecifies an offset to a luma quantization parameter Qp′_(Y) used forderiving Qp′_(CbCr) is coded.
 10. The device of claim 6, wherein thesyntax element that specifies the offset to the luma quantizationparameter Qp′_(Y) used for deriving Qp′_(CbCr) comprises apps_joint_cbcr_qp_offset syntax element.
 11. A method of encoding videodata, the method comprising: encoding, in an encoded video bitstream, asequence parameter set (SPS) referred to by one or more pictures ofvideo data, wherein encoding the SPS comprises: encoding, at a firstposition in the SPS, a syntax element that indicates whether jointcoding of chroma residuals is enabled or disabled for the one or morepictures of video data referring to the SPS; and encoding, at a secondposition in the SPS that is after the first position, one or more syntaxelements representing a quantization parameter (QP) mapping table; andencoding, in the encoded video bitstream, a picture parameter set (PPS)referred to by a picture of the one or more pictures of video data,wherein encoding the PPS comprises: encoding a syntax element thatindicates whether a QP offset for jointly coded chroma residuals isincluded in a chroma QP offset table and whether a syntax element thatspecifies an offset to a luma quantization parameter Qp′_(Y) used forderiving Qp′_(CbCr) is coded.
 12. The method of claim 11, wherein thesyntax element that indicates whether joint coding of chroma residualsis enabled or disabled for the one or more pictures of video datareferring to the SPS comprises a sps_joint_cbcr_enabled_flag syntaxelement.
 13. The method of claim 11, wherein the syntax element thatindicates whether a QP offset for the jointly coded chroma residuals isincluded in the chroma QP offset table and whether the syntax elementthat specifies the offset to the luma quantization parameter Qp′_(Y)used for deriving Qp′_(CbCr) is coded comprises apps_joint_cbcr_qp_offset_present_flag syntax element.
 14. The method ofclaim 11, wherein encoding the PPS further comprises: encoding, based ona value of the syntax element that indicates whether a QP offset forjointly coded chroma residuals is included in a chroma QP offset tableand whether a syntax element that specifies an offset to a lumaquantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) is coded: asyntax element that indicates whether the QP offset for jointly codedchroma residuals is included in a chroma QP offset table; and the syntaxelement that specifies an offset to a luma quantization parameterQp′_(Y) used for deriving Qp′_(CbCr) is coded.
 15. The method of claim11, wherein the syntax element that specifies the offset to the lumaquantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) comprises apps_joint_cbcr_qp_offset syntax element.
 16. A device for encoding videodata, the device comprising a memory configured to store at least aportion of an encoded video bitstream; and one or more processors thatare implemented in circuitry and configured to: encode, in the encodedvideo bitstream, a sequence parameter set (SPS) referred to by one ormore pictures of video data, wherein, to encode the SPS, the one or moreprocessors are configured to: encode, at a first position in the SPS, asyntax element that indicates whether joint coding of chroma residualsis enabled or disabled for the one or more pictures of video datareferring to the SPS; and encode, at a second position in the SPS thatis after the first position, one or more syntax elements representing aquantization parameter (QP) mapping table; and encode, in the encodedvideo bitstream, a picture parameter set (PPS) referred to by a pictureof the one or more pictures of video data, wherein, to encode the PPS,the one or more processors are configured to: encode a syntax elementthat indicates whether a QP offset for jointly coded chroma residuals isincluded in a chroma QP offset table and whether a syntax element thatspecifies an offset to a luma quantization parameter Qp′_(Y) used forderiving Qp′_(CbCr) is coded.
 17. The device of claim 16, wherein thesyntax element that indicates whether joint coding of chroma residualsis enabled or disabled for the one or more pictures of video datareferring to the SPS comprises a sps_joint_cbcr_enabled_flag syntaxelement.
 18. The device of claim 16, wherein the syntax element thatindicates whether a QP offset for the jointly coded chroma residuals isincluded in the chroma QP offset table and whether the syntax elementthat specifies the offset to the luma quantization parameter Qp′_(Y)used for deriving Qp′_(CbCr) is coded comprises apps_joint_cbcr_qp_offset_present_flag syntax element.
 19. The device ofclaim 16, wherein, to encode the PPS, the one or more processors areconfigured to: encode, based on a value of the syntax element thatindicates whether a QP offset for jointly coded chroma residuals isincluded in a chroma QP offset table and whether a syntax element thatspecifies an offset to a luma quantization parameter Qp′_(Y) used forderiving Qp′_(CbCr) is coded: a syntax element that indicates whetherthe QP offset for jointly coded chroma residuals is included in a chromaQP offset table; and the syntax element that specifies an offset to aluma quantization parameter Qp′_(Y) used for deriving Qp′_(CbCr) iscoded.
 20. The device of claim 16, wherein the syntax element thatspecifies the offset to the luma quantization parameter Qp′_(Y) used forderiving Qp′_(CbCr) comprises a pps_joint_cbcr_qp_offset syntax element.